The present invention relates to a concrete structure comprising at least two anchor rods coupled to one another, at least one of said anchor rods being provided with an external thread for that coupling. Such structures are generally known in the art. When producing large concrete structures it is frequently not possible to pour these in one piece. Therefore these are poured successively in parts. What is important here is that the reinforcement does form an essentially continuous structure. It is therefore customary in the art to fit, close to the boundary of the first part to be poured, a reinforcing rod provided with, for example, a threaded bush at the boundary surface. After pouring the casing is removed and the opening to the thread is exposed and an anchor rod, provided with an external thread, is screwed into this opening. The second part is then poured in contact with the first part and the strength of the structure is guaranteed by the connection continuing through the structure.
Stringent requirements are imposed on the anchor rods used.
In general such rods are produced by using reinforcing steel that has already been provided with raised portions or ribs as the starting material. After cutting to size, the relevant end of the reinforcing steel that has to be provided with a thread is butted. After all, insufficiency in cross-section at the location of the thread is not acceptable in a linking system. Butting of steel is carried out by heating the steel. By this means a substantial proportion of the material structure that was originally longitudinally oriented will be modified. After butting the material must be cooled under controlled conditions. It has been found that as a result of the increasingly extensive alloying of reinforcing steel, on the one hand, and the acceptance of an ever higher percentage of impurities (scrap) on the other hand, an inadmissible reduction in strength can occur if there is the slightest deviation from the norm for quenching. In particular this causes cracking. No problems have been found in the case of normal applications of reinforcing steel, that is to say where no heating and butting takes place, but the abovementioned problems are observed as soon as anchors provided with thread have to be produced.
It will be understood that cracking can ultimately lead to failure, which can have major consequences for structures in which such anchor rods can be used. Moreover, such anchor rods are used in prefabricated concrete components, as a result of which lifting slings and the like can be attached in a simple manner to the anchor rod. This gives rise to stress especially when moving the prefabricated elements concerned and failure can also have disastrous consequences here.
On the other hand, it is extremely important that anchor rods have a relatively low price for a relatively high quality.
EP 0816584A1 discloses a screw coupling for anchor rods having the features of the preamble of claim 1.
The aim is to eliminate the disadvantages known from the prior art with an improved anchor rod being placed in a concrete structure and with failure being virtually precluded.
This aim is achieved with a concrete structure as described above by the characterising measures according to claim 1.
The material structure of a metal anchor rod is understood to be, inter alia, the molecule/fibre/grain orientation of the material concerned.
It is pointed out that an anchor bolt is disclosed in U.S. Pat. No. 5,054,146. This bolt must be used in particular for anchoring the rod in boreholes, openings or the like made in rocky soils. The anchor rod concerned is introduced into such an opening and a synthetic resin material is then used to provide for adhesion between the rod and the surroundings. This anchor rod is provided with a pattern consisting of flattened sections pressed in of the material. These lobes serve as stirrers for stirring the resin by means of which the anchor rod is fixed to the structure.
Using the anchor rod according to the present invention it is possible to make concrete structures with which the risk of failure of the anchor rods is avoided as far as possible.
The pattern used according to the invention is a pattern that is customary for reinforcing steel, that is to say of shallow height and produced with a gradual transition with respect to the other part of the anchor material. This pattern is obtained with the aid of a simple rolling operation, which can be combined with the reduction in the circumference of the anchor rod.
According to an advantageous embodiment of the invention, the concrete structure comprises a first poured part with an anchor rod fitted therein, the end of which anchor rod is provided with an internal thread by means of which the one anchor rod is coupled, said one anchor rod is fitted in a second part poured in contact with said first poured part. Said internal thread can be implemented by means of a bush clamped on the anchor rod. However, it is also possible to use a rod material of relatively large diameter as the starting material, the external diameter approximately corresponding to the external diameter of the part in which the internal thread has to be made. The diameter of the other part of the rod is then reduced to a very appreciable extent in order to obtain the desired dimensions.
According to the invention such an anchor rod is preferably produced by providing a method for the production of an anchor rod comprising the provision of a length of steel rod, making a thread at one end and making a pattern on the other part of the rod, wherein the thread is preferably made by rolling a thread and wherein the pattern is made by rolling the relevant part of the rod after making the thread. Instead of rolling a thread, cutting can also be used. In such a case it is preferable to reduce the diameter of that part where there is no thread, and where the pattern has to be applied, by rolling. The strength and other mechanical properties improve as a result of this rolling operation. Pattern or relief is understood here to be any surface structure or raised portion by means of which the engagement of the anchor rod and the surrounding concrete is promoted.
According to the invention no longer a length of reinforcing steel is used as the starting material and a section of enlarged diameter is provided for the thread by butting, but that using a section of rod material the section provided with a pattern or ribs is obtained by rolling. That is to say the difference in diameter between the section provided with a thread and the section provided with a pattern is obtained not by increasing the diameter at the section provided with a thread but by reducing the diameter of the section provided with a pattern. It has been found that during such a rolling operation, which can be carried out cold, the mechanical properties of the anchor rod only improve and do not deteriorate in any way. Consequently it is possible to use a relatively low grade steel and nevertheless to achieve adequate strength as required in accordance with the standards.
Because butting now no longer takes place, the material structure of the steel in the core at the threaded section will be unchanged, that is to say will essentially match that of the original material structure of said anchor rod.
Using the method described above it is possible in a simple manner to produce anchor rods with relatively high strength from relatively low-alloy materials. Examples of such materials are types of steel which have a relatively high carbon content. Because, in contrast to the prior art, it is not necessary to carry out an annealing treatment with deformation (warm butting) in order to produce a thread, the structure of the steel material is not affected or is barely affected by the method according to the present invention.
Because it is now possible inexpensively to produce anchor rods from material of high strength, it is possible in the case of some applications to replace relatively thick anchor rods made of conventional steel by appreciably thinner anchor rods made of high-tensile material. In the case of structures subjected to heavy load, there is often the problem that anchor rods are close to one another, as a result of which it can no longer be guaranteed that concrete material, and in particular the aggregate contained therein, infiltrates between the reinforcing rods and thus provides adequate strength. By, in accordance with the invention, using reinforcing rods of high strength which have a relatively small diameter the infiltration of concrete material is guaranteed.
A further increase in the strength of the structure can be obtained by producing the thread by rolling. After all, a similar thread can be obtained with a smaller starting diameter. The diameter of the transition section will be smaller than the external diameter of the threaded section. Of course, as a result of the rolling, the material structure of steel in the thread will deviate from the initial structure of the anchor rod, but this has no effect on the material structure in the core thereof. If a thread is cut, the other section of the anchor rod can be cold-rolled in the manner described above without any problem.
According to the invention the section provided with a pattern has a very appreciable length compared with the length of the section provided with a thread.
The pattern can be any pattern known in the prior art, such as raised portions or ribs. These can be introduced simply during rolling using a profiling roller.
If the thread is used in combination with a bush, which can be either a separate coupling bush or a bush fitted on the end of another anchor rod, it can be advantageous for the transition section to have a shoulder against which such a bush bears, or to be fitted in a seating surrounding the shoulder.
The anchor rod described above can be produced from any steel material known in the state of the art, which material can be either structural steel or stainless steel. St 52.3, which is a type of steel which is relatively easy to obtain and has relatively high purity, is mentioned by way of example.
As indicated above, types of steel of relatively high strength, that is to say with tensile strengths of, for example, 1,100 N/mm2, can also be used.